Our Experience with MR Imaging of Perianal Fistulas

Magnetic resonance imaging in the workup of patients with perianal fistulas

Background

Perianal sepsis and fistulas are common lesions. Fistula-in-ano is a tedious problem because of high recurrence rates and severe unexpected complications postoperatively. Many imaging modalities are used to evaluate this area. Magnetic resonance imaging (MRI) has been considered the gold standard procedure for perianal fistula assessment, i.e., it provides the surgeon with an accurate roadmap to select the best surgical approach, determines the extent of sphincter division, and estimates the risk of postoperative incontinence. We carried out a prospective diagnostic accuracy study involving 50 patients (mean age, 42.44 years) with perianal fistulas who underwent pelvic MRI with a 1.5 Tesla scanner using multiple sequences, including diffusion and post-contrast series that were either local or systemic. This study aimed to evaluate the diagnostic validity of pelvic MRI/MR fistulogram in perianal fistula assessment, identify perianal fistula-associated findings by MRI, and optimize the MRI technique with maximum technical safety.

Results

Intersphincteric fistulas were the most common type of perianal fistula observed based on Parks’ classification. Intersphincteric, trans-sphincteric, extrasphincteric, and suprasphincteric fistulas were found in 30 (60%), 12 (24%), 4 (8%), and 4 (8%) patients, respectively. According to St. James’ classification, 21 (42%), 9 (18%), 8 (16%), 4 (8%), and 8 (16%) patients had perianal fistula grades I, II, III, IV, and V, respectively. The combination of variable MR sequences and MR fistulogram increased the diagnostic validity of MRI examinations. Our results correlated with surgical results (reference standard) with perfect interobserver reliability.

Conclusions

Of all imaging modalities, MRI has become a prerequisite for a successful surgery of a perianal fistula. MRI can identify: (a) fistula morphological details, (b) the relationship between the fistulous tract and the anal sphincter, (c) fistula wound healing, (d) an active versus chronic scarred fistula, (e) postoperative stigmata, and (f) a perianal fistula from its mimics. MRI with variable sequences and MRI fistulogram are successful combinations that increase diagnostic efficiency with technical safety by avoiding both ionizing radiation and systemic gadolinium.

Perianal fistulas: A review with emphasis on preoperative imaging

PURPOSE

We aim to present a comprehensive literature review which focuses on the preoperative imaging of perianal fistulas.

MATERIAL/METHODS

Pelvic magnetic resonance imaging (MRI) and endoanal ultrasound (EAUS) are the two first-line imaging modalities for the preoperative evaluation of patients with perianal fistulas. We conducted a search in PubMed, Scopus and Google Scholar concerning articles comparing pelvic MRI with EAUS, which were published from 1994 until 2019.

RESULTS

In most articles, pelvic MRI is superior to EAUS for the evaluation of perianal fistulas (especially for supralevator and extrasphincteric ones). Preoperative pelvic MRI is associated with statistically significant better results and prognosis after surgical treatment of the disease. Preoperative EAUS poses high sensitivity and specificity in identifying intersphincteric and transsphincteric perianal fistulas, as well as the internal opening of a fistula-in-ano. There is only one meta-analysis which compares the diagnostic accuracy of the two mentioned imaging modalities in preoperative fistula detection. Sensitivity of both - pelvic MRI and EAUS, is acceptably high (0.87). Specificity of pelvic MRI is 0.69 in comparison to EAUS (0.43), but both values are considered low.

CONCLUSIONS

Future well-designed prospective studies are needed to investigate the diagnostic accuracy of pelvic MRI and EAUS in the preoperative assessment of patients with perianal fistulas. Moreover, the combination of pelvic MRI and EAUS should also be studied, since several published articles suggest that it could lead to improved diagnostic accuracy. A novel treatment algorithm for perianal fistulas could arise from this study.

CT and MRI Evaluations in Crohn's Complications: A Guide for the Radiologist

Inflammatory bowel diseases (IBD) are a group of chronic inflammatory intestinal conditions with unknown etiology. Crohn's disease (CD) and ulcerative colitis (UC) are the two main types of IBD and they have some interchangeable and some different clinical and pathological characteristics. When diagnosis is performed for the first time, the majority of CD patients have a predominant inflammatory condition. As the disease progresses most patients experience the development of complications, such as abscesses, fistulas, perforation, strictures, and others. Both computed tomography (CT) and Magnetic Resonance Imaging (MRI) allow great view of the whole length of the intestinal tract together with the eventual extra-and intra-intestinal complications. MR enterography (MRE) and CT enterography (CTE), performed after oral administrations of contrast medium, have similar diagnostic accuracy for the diagnosis of CD and its complications. Even though CT is still the most familiar diagnostic technique used for studying CD worldwide, MRE have several important benefits that are leading to rapid increase in its employment in the last years. In particular, MRE allows a superior soft tissue contrast resolution compared to CT, offering a better visualization of bowel wall and its inflammatory and fibrotic characteristics. Moreover, Pelvic Magnetic Resonance is the principal technique in patients with perianal disease due to its ability of providing precise and fine detail images of the sphincter complex, which are crucial for evaluating pelvic disease. In this paper we describe common and uncommon complications in patients with CD, and explain how to identify their findings in CT and MR exams.

Perianal fistula mapping at 3 T: volumetric versus conventional MRI sequences

AIM

To evaluate volumetric contrast-enhanced three-dimensional T1-weighted (CE 3D T1) turbo spin-echo (TSE) with variable flip angle (SPACE), CE 3D T1 volumetric interpolated breath-hold examination (VIBE) sequences with conventional CE-two-dimensional (2D)-T1 and 2D-T2-weighted imaging (WI) sequences in assessing perianal fistulas.

METHODS AND MATERIALS

Twenty-three patients with perianal fistula were included in this prospective study and underwent pelvic magnetic resonance imaging (MRI) at 3 T including fat-supressed CE 3D T1 SPACE, CE 3D T1 VIBE, axial and coronal 2D-T1WI together with 2D-T2WI sequences in the axial and coronal planes. Acquisition times were recorded. Performance of each sequence was evaluated in terms of image quality, presence of artefacts, lesion conspicuity, fistula type, presence of abscess, visibility of internal orifice, and number of internal orifices. Results were compared with post-surgical findings defined as the reference standard.

RESULTS

Both CE 3D T1 VIBE and CE 3D T1 SPACE were the best sequences to determine fistula type and in terms of image quality, artefacts, and determining locations of internal orifices. The number of internal orifices was detected correctly in 23 (100%) patients for CE 3D T1 SPACE and CE 3D T1 VIBE sequences, in 17 (73.9%) patients on CE-T1WI, and in seven (30.4%) patients on 2D-T2WI. Lesion conspicuity was higher for CE 3D T1 SPACE and CE 3D T1 VIBE sequences compared to the 2D sequences (p<0.05). The overall acquisition time for each 3D sequence was shorter compared to the 2D sequences combined.

CONCLUSION

CE 3D T1 SPACE and CE 3D T1 VIBE sequences may outperform conventional 2D sequences in the evaluation of perianal fistulas in terms of visibility and number of internal orifices with a shorter scanning time.

MR imaging of perianal fistulas in Crohn's disease: sensitivity and specificity of STIR sequences

INTRODUCTION

Although some studies proved the role of STIR sequences in the evaluation of perianal fistulas in Crohn's Disease (CD), contrast medium is still injected in many institutions since there is not a validated reference MR protocol. Our purpose was to evaluate the role of the STIR sequence in the detection and characterization of perianal fistulae comparing it to the post-contrast T1 sequence and correlating it with rectal examination under anesthesia.

MATERIALS AND METHODS

We retrospectively reviewed all clinical records of 31 CD patients, suspected of having perianal fistulas, who had been submitted to an MR study before and after contrast medium injection and surgical exploration under anesthesia within the same month. Perianal fistulas were classified according to the Parks' criteria. Finally, comparison between STIR and post-contrast T1-weighted fat saturated sequences was done.

RESULTS

29 fistulas were detected in 25 patients who underwent an MR study. There was no significant difference between MR imaging and exploration under anesthesia. For the detection of perianal fistulas of any type, there was a perfect statistical agreement between gadolinium-enhanced and STIR sequences (kappa value = 1).

CONCLUSION

STIR sequences represent a valid alternative to the T1-weighted sequences acquired after the injection of contrast medium, allowing the identification of the primary fistula, any secondary ramification, and complications of the disease.

An interesting fistula tract presenting with recurrent gluteal abscess: instructive case

A fistula extending from the gluteus to penis is an extremely rare entity. In this paper, we have highlighted novel variant of congenital penile to gluteal fistula complicated with gluteal and penoscrotal abscess in a previously healthy boy. A fistulous tract extending from the gluteus to penis has been shown by fistulogram. Bleomycin has been used in fistula tract with successful results in our patient.